The main difference between sessions and cookies is that sessions are stored on the server, and cookies are stored on the user’s computers in the text file format. Cookies can not hold multiple variables,But Session can hold multiple variables.We can set expiry for a cookie,The session only remains active as long as the browser is open.Users do not have access to the data you stored in Session,Since it is stored in the server.Session is mainly used for login/logout purpose while cookies using for user activity tracking

There are two types of key of array. It can be numerical And associative.
Numerical :It stores each array element with numeric index name.
associative : It contains characteristic element or string index name.

Class:Classes are intended to represent those real-life items that coder like to manipulate within an application.
object: An instance of class is called object.

Property overloading continues to protect properties by forcing access and manipulation through public methods, yet allowing the data to be accessed as if it were a public property.

The most common and used way is to get data into a format supported by Excel. For example, it is possible to write a .csv file, to choose for example comma as separator between fields and then to open the file with Excel.